催化学报

催化学报

• •    

缺陷UiO-66催化剂在温和条件下实现甲烷高选择性氧化制乙酸

魏耀文a, 王建伟a, 郭皓a,*, 班涛a, 岳玉峰a, 胡地a,*, 黄海保a,b,*   

  1. a新疆大学化工学院, 新疆煤炭清洁转化与化工过程重点实验室, 新疆 乌鲁木齐 830046;
    b中山大学环境科学与工程学院, 广东 广州 510275
  • 收稿日期:2025-11-19 接受日期:2025-11-19
  • 基金资助:
    国家重点研发计划(2024YFC3713500); 新疆维吾尔族自治区重大科技专项(2024A03012012); 国家自然科学基金(22276223); 新疆维吾尔族自治区重点研发计划(2022B03029-3); 新疆维吾尔自治区人才项目“天池博士”计划(TCBS202013); 新疆维吾尔族自治区自然科学基金(2023D01C170).

Highly selective oxidation of methane to acetic acid enabled by deficient UiO-66 under mild conditions

Wei Yaowena, Wang Jianweia, Guo Haoa,*,ban Taoa, Yue Yufenga, Hu Dia,*, Huang Haibaoa,b,*   

  1. aXinjiang Key Laboratory of Coal Clean Conversion & chemical Engineering Process, School of Chemical Engineering and Technology, Xinjiang University, Urumqi 830046, Xinjiang, China;
    bSchool of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, Guangdong, China
  • Received:2025-11-19 Accepted:2025-11-19
  • Supported by:
    National Key Research and Development Program of China (2024YFC3713500), Major Science and Technology Projects of Xinjiang (2024A03012), the National Natural Science Foundation of China (22276223), the support of the Key Research and Development Plan of Xinjiang (2022B03029-3), the “Tianchi Talents” Introduction Plan (TCBS202013), and the Natural Science Foundation of Xinjiang Uygur Autonomous Region (2023D01C170).

PDF

27

摘要： 在温室效应持续加剧的形势下,甲烷作为高效温室气体,其排放治理与资源化利用已成为减排领域的关键议题.与此同时,甲烷又是储量丰富的清洁碳源,若能实现高选择性催化转化,可在“控排放-增价值”之间建立协同路径.甲烷分子惰性源于高键能C-H键,使得温和条件下的选择性活化与定向转化长期受限,相较于甲烷制合成气及甲醇等C1路线,直接生成乙酸等C2含氧化学品兼具更高的经济附加值与潜在的过程减碳优势.然而,该过程面临双重瓶颈:一是活化初始C-H键需要高效且可控的活性氧物种;二是后续C-C偶联与氧化深度难以协同调控,易导致过氧化生成CO2或形成多种副产物.因此,构建具备可调微环境、能够同时调控氧化剂活化与关键中间体稳定的异相催化体系,是实现甲烷温和选择性氧化制乙酸的核心科学问题.
本工作以UiO-66为模型MOF,提出“配体缺陷诱导的本征Zr活性中心重构”策略:通过在合成过程中引入三氟乙酸(TFA)竞争配位,调控“缺失配体”缺陷,暴露配位不饱和Zr4+位点,从而在无需外加异金属的条件下建立清晰的本征活性中心.结构表征表明,使用适量TFA调控可在保持UiO-66骨架衍射特征的同时引入可控缺陷;其中UiO-66-0.3T呈现更高孔结构可及性与缺陷有序化特征,比表面积达到1043.3m2 g-1,并由热重定量得到Zr6节点配位缺失数约为4.98.X-射线光电子能谱与电子结构分析显示,缺陷调控引发Zr位点电子结构重构,表现为Zr 3d相关d带中心上移,有利于增强对氧化剂与甲烷的界面电子耦合.在以H2O2为氧化剂的甲烷选择氧化反应中,TFA调控后的UiO-66-XT整体优于本征UiO-66,并呈现随缺陷程度变化的“火山型”性能相关性.在最佳条件下(150°C,6h,30bar CH4,10mL 5 wt% H2O2,30mg催化剂),UiO-66-0.3T实现含氧产物总产率1971μmol gcat.-1,其中乙酸产率1691μmol gcat.-1,乙酸选择性高达84%;催化剂在至少5次循环中保持稳定.温度与H2O2浓度的系统考察进一步表明,升温可促进乙酸生成,但超过150°C后过氧化趋势增强,CO2增多且选择性下降;H2O2浓度在5wt%附近达到最优,过量氧化剂会导致含氧产物深度氧化.通过电子顺磁共振(EPR),原位漫反射红外光谱(DRIFTS)及密度泛函理论(DFT)计算阐明了反应机理:EPR直接观察到催化剂在H2O2体系中高效生成•OH,并在引入CH4后出现•CH3信号,说明缺陷Zr位点促进H2O2活化并触发甲烷C-H键断裂;原位DRIFTS检测到*OH,*COOH与*CH3COOH等关键表面物种的生成与积累,显示反应主要沿“缺陷位点上活性氧供给-甲烷定向活化-COOH稳定-C-C偶联”路径进行;DFT计算给出UiO-66-0.3T对CH4与H2O2的吸附能分别为-0.63与-2.94eV(UiO-66为-0.54与-1.89eV),并通过电荷重分布与轨道耦合增强解释了其更高的H2O2分解与甲烷活化能力.由此可见,缺陷诱导的电子结构重构与位点可及性提升实现了活性氧生成,甲烷活化与C-C偶联的协同调控,进而显著提升乙酸选择性与产率.
综上,本研究通过缺陷工程激活MOF骨架中金属团簇的本征催化潜力,在温和条件下实现甲烷向C2含氧化学品的定向转化.未来可围绕缺陷类型及空间分布的精准调控,反应微环境与自由基通量的定量关联及连续化反应体系适配开展深入研究,为温和条件下甲烷高值利用催化剂的设计提供可推广范式.

关键词: 甲烷, 选择性氧化, 乙酸, UiO-66催化剂, 缺陷工程

Abstract: The direct conversion of methane (CH4) into higher-value C2 products is essential for the green and efficient conversion of clean energy. However, this conversion process faces significant challenges due to the difficulty in activating methane's C-H bonds and the complexity of controlling C-C coupling reactions. Herein, we design and construct the unsaturated metal Zr4+ site by introducing ligand defects in UiO-66 through treatment with trifluoroacetic acid (TFA), which enables the direct oxidation of methane to acetic acid using H2O2 under mild conditions. Remarkably, a volcano-shaped correlation was observed between the degree of ligand defects in UiO-66 and acetic acid selectivity. Under optimal conditions (150 °C), the catalyst achieved an outstanding acetic acid selectivity of 84% with a high yield of 1691 μmol·gcat.-1. Notably, the catalyst exhibited exceptional stability, maintaining its performance over at least five consecutive reaction cycles. Through TFA modulation, the d-band center of the Zr 3d orbital in Zr4+ sites exposed by UiO-66 shifts upward. This promotes the decomposition of H2O2, thereby facilitating the formation and stabilization of highly reactive Zr-OH species, which enhances the activation of C-H bonds in CH4. The resulting *CH3 species is further oxidized by *OH species into *COOH species, which undergo stable C-C coupling at exposed Zr4+ sites to produce acetic acid. This work provides novel insights into the design of highly efficient catalysts for the direct conversion of methane into C2 oxygenates compounds under mild conditions.

Key words: Methane, Selective oxidation, Acetic acid, UiO-66 catalyst, Defect engineering